Semiconductor materials have been used in a broad range of applications, including logic gates, sensors, solar cells, and many other applications. These materials form the backbone of modern electronic applications. Many of these applications capitalize on the semiconducting nature of the material to perform a function that involves flowing electrons.
Typically, electron flow in and out of the active semiconductor region involves a semiconductor-metal interface. This semiconductor-metal interface is often characterized by a contact resistance, which is notoriously difficult to reduce. This contact resistance of the interface degrades the overall efficiencies of the device due to poorly matched or connected electrical contacts between the metal and the semiconductor. It is often difficult to have metal adhere to certain semiconductor materials and there are often impurities, defects, etc. that are between the metal contact and the underlying semiconductor. Furthermore, additional layers are often required to impede the diffusion of materials from the metal region to the semiconductor region. Semiconductor materials are typically in the form of a crystal lattice structure, through which it is often easy to diffuse metallic atoms. Hence a layer is typically used to separate the metal contact from the semiconductor region so as not to dope the semiconductor with metallic ions via the diffusion process.